Generally, this kind of derailleur basically comprises a pantograph mechanism of four members: a base member, two linkage members and a movable member having a chain guide.
Such a derailleur, however, forms a large space between the four members to result in a bad appearance.
Hence, in the Japanese Patent Laid-Open Gazette No. Sho 58-53,587, a derailleur has hitherto been proposed which interposes between the base member and the movable member one linkage of a box-like shape and having a lid, and contains the other linkage member of a rod-like shape in the aforesaid box-like-shaped linkage member to thereby make a good appearance.
The box-like-shaped linkage member, however, contains therein a crank plate together with the rod-like linkage member retained thereto, so that the latter is difficult to incorporate in the box-like-shaped linkage member. As a result, a problem is created in that the workability for the manufacturing is poor and the manufacturing cost is high.
Furthermore, the conventional derailleur employs one box-like linkage member, but a control wire to actuate the movable member is fixed to the box-like linkage member through a well-known wire-holder which has a tightening screw and projects from the linkage member.
Hence, the wire holder projecting from the box-like linkage member makes an ill appearance and the control wire is tightened by the screw to be insufficient in its fixing length. As a result, even if the screw is fully tightened, the wire, after repeated operations, may escape from the holder due to a weakened fixing strength, and is liable to be broken at the fixing point. Also, the special wire-fixture largely projecting from the linkage member is an obstacle to a cyclist and the derailleur is complicated in construction, large-sized, and expensive to produce.